[0001] This invention relates to fluid flow control apparatus for compressible or incompressible
fluids including a fluid flow governor, particularly, though not exclusively, for
use in controlling the pressure at an entry point to a distribution system or sub-system
for water, for example.
[0002] When the demand for water by consumers is large the pressure drop in a water distribution
system between the entry point and distant points of the system is considerable. Maintaining
the entry point pressure at all times at the level necessary to provide adequate pressure
at the distant points for periods of high demand can result, during periods of low
demand, in excessive pressure at consumers' premises even at distant points and waste
of water by unnecessary consumption and by leakage which i.s almost inevitable. Under
low demand conditions not only does leakage form a higher proportion of the total
demand but investigation has shown that some leak orifices can actually increase in
area with pressure, so aggravating the problem if excessive pressures are maintained
at all times.
[0003] . It is one object of the present invention to provide fluid flow control apparatus
which can be used in such a water distribution system to modify the governed pressure
at the entry point to compensate for changes in flow.
[0004] It is another object of the invention to provide a sensitive pressure reducing valve
which responds rapidly to changes in governed pressure fluctuations with less tendency
to hunt than conventional sensitive pressure reducing valves.
[0005] The present invention consists in fluid flow control apparatus, for controlling the
flow of fluid through a pipe, comprising a fluid flow governor; in the pipe, a fluid
flow control valve controlled by the governor and producing, in operation, a control
pressure at a predetermined location in the pipe downstream of the valve; and means
for producing, in operation, a differential pressure derived from a characteristic
of fluid flow in the pipe, the fluid flow governor having a first pressure-responsive
element to which the differential pressure is applied, spring means acting on the
first pressure-responsive element in opposition to the differential pressure, a second
pressure-responsive element to which the control pressure is applied, means for loading
the second pressure-responsive element in opposition to the control pressure and means
for combining displacements of the two pressure-responsive elements to control the
setting of the fluid flow control valve.
[0006] The governor may be coupled directly to the fluid flow control valve which will then
be of a kind in which the extent of valve opening is varied by the governor.
[0007] Alternatively the governor may be indirectly coupled to the fluid flow control valve
by servo means which may comprise, as the element to which the governor is to be directly
coupled, a pilot valve in a hydraulic or pneumatic servo system, or a switch in an
electrical servo system.
[0008] When the fluid flow control apparatus is intended to afford compensation for changes
in flow, the characteristic of fluid flow from which the differential pressure is
derived may be the rate of fluid flow through the pipe.
[0009] The fluid flow control apparatus may alternatively be intended to serve as a sensitive
pressure reducing valve. The characteristic of fluid flow from which the differential
pressure is derived may then be the rate of change of fluid pressure at a specified
region in the pipe.
[0010] When the fluid flow control apparatus is to compensate for changes in flow, the means
for producing the differential pressure comprises a device producing (in operation)
a pressure which is lower than a pressure upstream of the device (the higher pressure),
the difference between the higher pressure and the lower pressure being the differential
pressure.
[0011] The said device may be an orifice plate in the pipe, the higher pressure being that
upstream of the orifice plate and the lower pressure that in the region of the throat
of the orifice plate.
[0012] The higher pressure and the lower pressure may be applied to opposed areas of the
first pressure-responsive element, the resultant fluid pressure acting on the first
pressure-responsive element being the differential pressure.
[0013] Where the characteristic of fluid flow from which the differential is derived is
the rate of change of fluid pressure, the means for producing the differential pressure
may comprise two impulse connections, one. to each of opposed areas of the first pressure-responsive
element, from the specified region of the pipe, one of the impulse connections including
restricting means for producing at the first pressure-responsive element on change
of pressure at the region (in operation), a pressure which is lower than the pressure
(the higher pressure) in the other impulse connection, the difference between the
higher pressure and the lower pressure being the differential pressure.
[0014] Whatever the characteristic of fluid flow from which the differential pressure is
derived, the fluid flow control apparatus may include an impulse connection including
a throttling device through which fluid pressure is applied to the first pressure-responsive
element. The fluid pressure affected by the throttled impulse connection may be one
of the components of the differential pressure. The restriction imposed by the throttling
device affects the speed of response to changes in the characteristic of fluid flow,
preferably without affecting the speed of response to changes in the control pressure.
The throttling device may be adjustable; a needle valve, for example.
[0015] The invention further consists in a fluid flow governor for use in fluid flow control
apparatus for controlling the flow of fluid through a pipe which includes a fluid
flow control valve which the governor is adapted to control and means in the pipe
for producing, in operation, a differential pressure derived from a characteristic
of fluid flow in the pipe, the governor comprising a first pressure-responsive element,
spring means for biassing the first pressure-responsive element, a second pressure-responsive
element, means for loading the second pressure-responsive element, means for enabling
the differential pressure to be applied to the first pressure-responsive element in
opposition to the spring means, means for enabling a control pressure to be applied
to the second pressure-responsive element in opposition to the loading thereon and
means for combining displacements of the two pressure-responsive elements and adapted
to control the setting of the fluid flow control valve.
[0016] The displacements of the two pressure-responsive elements may be combined at actuating
means coupled to the fluid flow control valve or to servo means for actuating the
fluid flow control valve.
[0017] In one form of apparatus according to the invention the first pressure-responsive
element is operatively coupled to the actuating means and the second pressure-responsive
element is operatively coupled to the first pressure-responsive element through the
spring means, the first and second pressure-responsive elements being open to a first
chamber in the sense that in operation forces on the pressure-responsive elements
due to pressure in the first chamber oppose the spring means, the first pressure-responsive
element being open to a second chamber in the sense that, in operation, the first
pressure-responsive element is subjected to the differential pressure resulting from
the difference in pressures in the first and second chambers, and the second pressure-responsive
element being loaded in the sense to oppose, in operation, pressure applied to the
second pressure-responsive element in the first chamber.
[0018] In operation of such a system the higher pressure acting on the second pressure-responsive
element controls directly or indirectly movement of the fluid-flow control valve to
correct the governed pressure.
[0019] The first pressure-responsive element is subjected to the difference between the
higher pressure and the ' lower pressure. The deflection of the spring means is dependent
upon this pressure difference and alters the relative positions of the first and second
pressure-responsive elements and therefore affects the fluid-flow control valve through
the actuating means which is directly coupled to the first pressure-responsive element
to modify the governed pressure in accordance with this pressure difference. The pressure
difference depends on the rate of flow through the main or pipe and the governed pressure
is thus flow compensated.
[0020] Alternatively the displacements of the two pressure-responsive elements may be combined
at fluid flow valve means having first and second relatively movable elements which
co-operate to define a closed or neutral position, the first pressure-responsive elements
being operatively connected to the first relatively movable elements and the second
pressure-responsive element being operatively connected to the second relatively movable
elements. The relatively movable elements may be a valve body and a valve member movable
therein.
[0021] The first and second pressure-responsive elements are preferably of equal effective
area. A preferred form of pressure-responsive element is a flexible diaphragm but
any other suitable known type of pressure-responsive element may be used such as a
piston and cylinder or a bellows.
[0022] A combination of different types of pressure-responsive element could be used. For
example, in the first form of apparatus according to the invention referred to above,
the second pressure-responsive element may be a diaphragm and the first pressure-responsive
element a bellows open at one end, the open end being connected to a movable part
of the diaphragm so that the bellows is free to move relative to a housing of the
governor. The diaphragm covers the open end and the first chamber is the interior
space defined by the diaphragm and the internal surface of the bellows, the bellows
being provided with means for applying pressure to the interior space. The second
chamber surrounds the bellows. The bellows may be made of spring metal or other resilient
material. The inherent resilience of the bellows may then enable the bellows to serve
as, or at least complement, the spring means.
[0023] The spring means, unless constituted by the bellows, could be an air spring but is
conveniently a coil spring with open coils normally loaded in tension but stiff enough
and with its end coils stably supported so as to be capable, when required, of transmitting
a compressive load, in the manner of a strut.
[0024] The second pressure-responsive element may be loaded by a compression spring. The
stiffness of the compression spring is greater than that of the spring means, preferably
within the range of two to eight times, for example four times, the stiffness of the
latter. The greater the ratio of the stiffness of the compression spring to that of
the spring means, the greater the effect of the difference in pressures in the first
and second chambers on the displacement of the actuating means of the governor.
[0025] An embodiment of the invention will now be described, by way of example only, with
reference to the accompanying diagrammatic drawings, in which:-
Figure 1 is a sectional view of one form of fluid-flow governor for fluid-flow control
apparatus according to the invention,
Figure 2 shows fluid-flow control apparatus for a water main or pipe and including
the fluid-flow governor of Figure I, and
Figure 3 is a sectional view of a modified fluid-flow governor.
[0026] The governor of Figure 1 has a housing 1 comprising a body portion 2, a top cover
3 and a bottom cover 4. Between the body portion 2 and the bottom cover 4 a first
flexible, diaphragm 5 is clamped and between the body portion 2 and the top cover
3 a second flexible diaphragm 6 is clamped. The first and second diaphragms, which
are of equal effective area, are coupled by a tension spring 7. The tension spring
7 is open-coiled but is sufficiently stiff to be able, if required, to transmit a
compressive load. The end coils of the spring 7 are rigidly anchored to their associated
diaphragms. The second diaphragm 6 is loaded by a compression spring 8 housed in a
turret portion 9 of the top cover 3. The loading of the spring 8 on the second diaphragm
is variable by means of an adjusting screw 10. The first diaphragm 5 is secured to
a stem 11 which passes out of the bottom cover 4 through a gland 12 and is connected,
in this example, to a slidable valve member 13 of a pilot valve 14 of a servo-system
for operating a fluid flow control valve to be described later. The stem 11 constitutes
actuating means by which the governor exerts its control.
[0027] The diaphragms divide the interior of the housing 1 into three chambers, an intermediate
chamber 16 (constituting a first chamber) between the two diaphragms which is open
to a first impulse pipe 17 including a needle valve 18, a lower chamber 19, (constituting
a second chamber) below the first diaphragm 5 and open to a second impulse pipe 20
and an upper chamber 15 above the second diaphragm 6 which is vented to atmosphere.
[0028] The valve member 13 is slidable in a valve chamber 21 in a body 22 of the pilot valve
14. From the chamber 21 open three ports 23, 24, 25 which in the intermediate position
of the valve member 13 shown in Figure 1 are isolated one from another. Upward movement
of the stem 11 from the intermediate position shown connects ports 23 and 24, downward
movement connects ports 24 and 25.
[0029] In Figure 2 the reference 26 indicates the water main which is connected at one end
27, the upstream end, to a supply of water under pressure. The downstream end 28 of
the main 26 leads to the distribution pipes of the district being served. The pipe
includes a flow control valve 29, in this instance a fluid-pressure controlled valve
manufactured by M.I.L. Limited and known as the INBAL valve which comprises a valve
housing 30, an ovoid core 31 and a resilient sleeve 32 surrounding the core 31 and
sealed at both ends to the valve housing 30, forming an annular control chamber 33
between the sleeve 32 and the wall of the housing 30.
[0030] In the absence of pressure at the upstream end 27 of the main 26 the sleeve 32 is
urged by its own resilience onto the core 31 and the valve 29 is closed as shown by
the full lines in Figure 2.
[0031] If the control chamber 33 is open to atmosphere, pressure at the upstream end 27
of the main will cause the sleeve 32 to move away from the core 31 against the wall
of the valve housing 30 as shown in broken lines in Figure 2.
[0032] To regulate water flow through the valve 30 line water pressure from a tapping 34
in the upstream end 27 of the main 26, that is to say upstream of the flow control
valve 29, can be applied to the control chamber 33 under the control of the pilot
valve 14. The tapping 34 is connected by a pipe 35 to the port 23 of the pilot valve
14. Port 24 is connected by a pipe 36 to the control chamber 33. Port 25 is open to
waste at atmospheric pressure. It will be understood that when the stem 11 and the
valve member 13 are moved upwards line pressure is applied through pipes 35, ports
23 and 24 and pipe 36 to the control chamber tending to close the flow control valve
29. Return of the valve member 13 to the mid-position traps water in the control space
33 and the flow control valve 29 is retained at the particular setting reached. Downward
movement of the valve member 13 from the mid-position opens the control chamber 33
through pipe 36 and ports 24 and 25 to atmospheric pressure, allowing pressure of
water flowing through the flow control valve 29 to expand the sleeve 32. Water displaced
from the control chamber 33 drains to waste through port 25.
[0033] Downstream of the flow control valve 29 the main 26 is provided with an orifice plate
37 the throat of which is connected to the second impulse pipe 20. A tapping 38 between
the flow control valve 29 and the orifice plate 37 is connected to the first impulse
pipe 17.
[0034] In service, water pressure upstream of the orifice plate (higher pressure) is supplied
through the first impulse pipe 17 to the intermediate chamber 16 and applied to the
upper side of the first diaphragm 5 and the underside of the second diaphragm 6. Pressure
at the orifice plate throat tapping (lower pressure) is supplied through the second
impulse pipe 20 to the lower chamber and applied to the underside of the first diaphragm
5 which is thus subject to the difference in pressures at the orifice throat and upstream
of the orifice. At very low flows in the main 26 this differential pressure is insignificant
and has no effect on the first diaphragm 5. The pressure upstream of the orifice plate
on the second diaphragm 6 exerts an upward force on the second diaphragm which moves
upwards until this upward force and downward force due to compression of the spring
8 are equal. As in the absence of differential pressure across the orifice there is
no restraint on movement of the first diaphragm 5, the tension spring 7 remains at
its natural length, moves bodily upwards with the second diaphragm 6 and causes the
first diaphragm 5 to follow the movement of the second diaphragm. The resulting upward
movement of the stem 11 and valve member 13 connects ports 23 and 24 applying main
pressure from upstream of the control valve 29 to the control chamber 33 and begins
to close the control valve 29 to reduce the control pressure in the main 26 upstream
of the orifice plate 37 until the reduction in pressure on the underside of the second
diaphragm 6 and its resulting downward movement is sufficient to return the valve
member 13 to the mid- position. This stops the flow of water into or out of the control
chamber 33, the control valve 29 is held at the opening it has reached and the system
is in equilibrium. If the control pressure should fall below the predetermined pressure,
the first diaphragm moves downwards so that the valve member 13 connects ports 24
and 25 allowing water to escape to waste from the control chamber 33 increasing the
opening of the flow control valve 29 to restore the governed pressure.
[0035] Under these conditions of very low flow in the main 26, therefore, the governor acts
simply as a normal pressure governor monitoring and maintaining the required control
pressure at the location of the tapping 38 upstream of the orifice plate 37.
[0036] At higher flows through the orifice plate 37 the pressure at the orifice throat applied
to the underside of the first diaphragm 5 will fall below the control pressure upstream
of the orifice plate, applied to the upper side of the first diaphragm 5. The first
diaphragm 5 moves to extend the tension spring 7 until the spring force equals the
force due to differential pressure of the first diaphragm 5. It will be understood
from this that the extension of the tension spring 7 is proportional to the differential
pressure due to flow through the orifice plate 37.
[0037] This extension of the tension spring 7 alters the distance of the valve member 13
from the second diaphragm 6. The valve member 13 will then return to its mid-position
only when the second diaphragm is higher than under low flow conditions, that is,
when the control pressure has risen sufficiently to cause the second diaphragm to
increase the compression of the spring 8. As demand for water rises and the resulting
flow through the orifice plate increases the differential pressure applied to the
first diaphragm 5, the control pressure at the location in the pipe at which the tapping
38 is made will be increased in proportion to the differential pressure. The differential
pressure at an orifice plate varies as the square of the flow through it. Similarly,
the friction losses in a pipework system vary approximately as the square of the flow.
[0038] The entry to the water distribution system may be regarded as a point sufficiently
far downstream of the orifice plate 37 for velocity head at the throat of the orifice
plate to have been recovered. The governed pressure, that is to say, the pressure
required at such an entry point is in this instance directly dependent upon the control
pressure at the location of the tapping 38. Varying the governed pressure at the entry
to the distribution system in proportion to the differential pressure at an orifice
plate will enable a satisfactory delivery pressure to be maintained at the far end
of the distribution system with varying flows. The facility this provides of enabling
the governed pressure to be reduced substantially when the demand for water is low,
for example at night, is particularly useful in avoiding waste of water at leaks in
the distribution system.
[0039] The needle valve 18 is provided to enable the response of the governor to changes
in flow to be delayed. Its effect may be understood by considering the following situation.
[0040] If at some stage when the system is in equilibrium the needle valve 18 is completely
closed, water is trapped in the intermediate chamber 16. Relative movement between
the diaphragms 5 and 6 is prevented but the two diaphragms will move in unison in
response to changes in pressure in the lower chamber 19 and under the control of the
compression spring. The system is thus equivalent in this situation to a normal pressure
reducing valve controlling the pressure at the throat of the orifice plate 37. Any
increase in pressure at the throat will lift the diaphragms 5 and 6 raising the valve
member 13 of the valve 14 to admit pressure from port 23 to port 24 and increase the
pressure in the control space 33 tending to reduce the opening of the flow control
valve 29 and lower the downstream pressure. A reduction in pressure at the throat
will move the valve member 13 in the opposite direction to enlarge the opening of
the flow control valve 29 and increase the pressure at the throat. Provided the impulse
pipe 20 is unrestricted the response to changes in pressure at the throat will be
rapid.
[0041] The effect of opening the needle valve very slightly will be to allow water to flow
into or out of the intermediate chamber 16 very slowly in response to changes in the
differential pressure in the impulse pipes 17 and 20 that is to say the difference
between the higher pressure upstream of the orifice plate 37 and the lower pressure
at the throat which is dependent on the rate of flow through the main 26. There will
be a gradual adjustment of the equilibrium position, the rate of adjustment in response
to the differential pressure across the orifice plate 37 being controlled by the amount
of throttling at the needle valve 18. For any setting of the needle valve the response
to pressure will continue to be rapid.
[0042] Instead of a single, simple tension spring 7 a compound spring may be provided so
that the amount of compensation for change of flow will be something other than a
direct proportion of orifice plate differential.
[0043] By limiting the expansion of spring 7, for example by an internal tie, the range
of compensation can be limited to a fixed value. The system would continue to operate
as a pressure reducing valve responsive to changes in pressure upstream of the orifice
plate 37, but further increases in orifice plate differential would not raise the
control pressure which the system was aiming to achieve.
[0044] A fluid flow governor according to the invention may serve as a very sensitive pressure
reducing valve without flow compensation. For such a use the pressures applied to
the first or intermediate chamber 16 and the second or lower chamber 19 are taken
from the same point but through separate impulse pipes 17 and 20 as previously described,
the impulse pipe 17 including the needle valve 18 adjusted to be very nearly closed.
[0045] When conditions are constant the pressure in the chambers 16 and 19 will be the same.
With no differential pressure on the diaphragm 5, the spring 7 will be at its natural
length and the control pressure is under the control of the diaphragm 6 and spring
8. If the control pressure changes there will be an immediate and corresponding change
of pressure in the chamber 19 but only a slow change of pressure in the chamber 16.
This produces a differential pressure on the diaphragm 5 which responds rapidly under
the control of the relatively low stiffness spring 7 alone to move the pilot valve
member 13 markedly in the direction to correct the control pressure. The pressures
in the chambers 16 and 19 will gradually equalise so that the diaphragm 6 moves towards
the new position corresponding to the altered pressure in the chamber 16. The differential
pressure on the diaphragm 5 becomes less so that the control pressure is again mainly
under the control of the diaphragm 6. The governor can thus provide a pressure reducing
valve capable of responding rapidly to control pressure fluctuations with less tendency
to hunt than conventional sensitive pressure reducing valves.
[0046] In Figure 3 parts corresponding to those in Figure 1 bear the same reference numerals
and, if not specifically mentioned in the following description, are similar in construction.
The main differences in the fluid-flow governor of Figure 3 from that of Figure 1
are that the pilot valve 14 replaces the spring means 7 as the link between the diaphragms
5 and 6; the diaphragms have separate compartments in the housing I; and the spring
means 7 is anchored to the housing 1 instead of to the second diaphragm 6.
[0047] A body portion 2' of the housing comprises an upturned cup portion 40 and an inverted
cup portion 41 rigidly secured together, for example, by stays 42. The top cover 3
is similar to the top cover in Figure 1. A bottom cover 4' is similar to the top cover
3. The first diaphragm 5 is clamped between the cup portion 41 and the bottom cover
4' and the second diaphragm 6 is clamped between the cup portion 40 and the top cover
3. The stem 11 connected to the valve member 13 of the pilot valve 14 is in the embodiment,
connected directly to the second diaphragm 6 and passes out of the housing through
a gland 43 in the cup portion 40.
[0048] A rod 44 connected to the first diaphragm 5 extends upwards through a gland 45 in
the cup portion 41 and is secured to the body 22 of the valve 14 which, in this embodiment
is free to move relative to the housing 1, pipe connections to its ports 23, 24 and
25 being made by flexible hoses (not shown).
[0049] The spring means 7, which is similar to the spring means 7 of Figure 1 except that
it need not be capable of transmitting a compressive load, is housed in a turret portion
53 of the bottom cover 4 and is anchored to a cap 54 at the lower end of the turret
portion 4'. The cap 54 is preferably adjustably mounted on the turret portion 53 to
enable the tension of the spring means 7 to be varied.
[0050] The upper chamber 15 above the second diaphragm 6 is vented to atmosphere as in the
embodiment of Figure 1. A chamber 46 formed by the interior of the cup portion 40
and the second diaphragm 6 is connected by an impulse pipe 47 to a location in a main
or pipe at which a control pressure is to be monitored. A chamber 48 formed by the
interior of the cup portion 41 and the first diaphragm 5 is open to an impulse pipe
49. A chamber 50 formed by the bottom cover 4 and the first diaphragm 5 is open to
an impulse pipe 51 which includes a needle valve 52 for imposing an adjustable restriction
in the impulse pipe 51.
[0051] The impulse pipes 49 and 51 are connected to the means for producing the differential
pressure, impulse pipe 49 to the lower pressure component and impulse pipe 51 to the
higher pressure. The needle valve 52 enables the rate to be varied at which the governor
responds to changes in differential pressure.
[0052] The impulse pipes 47, 49 and 51 may be connected independently of one another and
as described above. The means for producing the differential pressure need not be
at the location at which pressure is being monitored by the impulse pipe 47. For example,
in a flow control system compensating for rate of flow as shown in Figure 2, the orifice
plate 37 could be in a region of the pipe upstream of the flow control valve 29. It
will generally be convenient to use as one of the component pressures of the differential
pressure the control pressure at the location at which pressure is being monitored
and then the impulse pipe 47 can be combined with one of the other impulse pipes 49,
51. For example, in apparatus equivalent to that shown in Figure 2 but using the governor
of Figure 3, impulse pipe 47 would be combined with the impulse pipe 51 and connected
to the tapping 38 in Figure 2, the impulse pipe 49 being connected to the throat of
the orifice plate 37.
[0053] The operation of the governor of Figure 3 in the context of apparatus of Figure 2
may, perhaps, be more easily explained by comparison with the operation of the apparatus
using the governor of Figure 1.
[0054] Where the governor of Figure 1 is used in the apparatus of Figure 2, at very low
flows there is no pressure difference across the diaphragm 5 and this floats unrestrained.
The spring means 7 remains at its natural length and simply acts as a link between
the diaphragm 6 and the valve rod 11. The diaphragm 6 can be regarded, at low flows,
as a simple pressure reducing valve, moving the valve 14 about its neutral position
to keep the control pressure on the underside of the diaphragm 6 constant. While the
valve 14 is in its neutral position, the setting reached by the flow control valve
29 does not change. At higher flows the pressure drop across the orifice acts on the
diaphragm 5 to extend the spring 7. The valve 14 will then only reach its neutral
position when the diaphragm 6 has been raised by an increase in the control pressure
to compress the spring 8 more. In this way the governor acts to raise the control
pressure and the governed pressure at high flows.
[0055] In the modification of Figure 3 the two diaphragms 5 and 6 are arranged in separate
compartments. The spring 8 directly loads the diaphragm 6 against the control pressure
as before. The pressure drop across the orifice still produces a pressure difference
across the diaphragm 5 to load the spring means 7. But the spring means 7 instead
of linking the diaphragms directly is anchored to the housing, and the displacements
of the diaphragms are combined at the valve means, the diaphragm 6 being connected
to the valve member 13 and the diaphragm 5 to the body of the valve 14.
[0056] Control pressure is still directly applied to the diaphragm 6 to compress its loading
spring 8 but the diaphragm now moves the valve member 13 directly. The neutral position
of the valve 14 is altered by moving the body 22 of the valve 14 relative to the valve
member 13. The movement of the valve body by the diaphragm 5 depends on rate of flow
and the spring rate of the spring means 7.
[0057] In this example the control pressure being monitored and kept constant under given
flow conditions is the governed pressure, that is to say the pressure required, for
example, at the entry to the distribution system downstream of the orifice plate to
meet distribution needs. In some circumstances it may be preferred to use the lower
pressure component of the differential pressure as the control pressure. This may
be done by combining the impulse pipe 47 with the impulse pipe 49. If, for example,
this combined connection is made to the throat of the orifice plate 37 in Figure 2,
the governed pressure is not directly proportional to the control pressure but, though
equal to it at very low flows, becomes higher than the control pressure at high flows
because of the recovery of velocity head well downstream of the orifice plate 37.
Greater compensation for rate of flow may be obtained by such an arrangement and may
be advantageous in some circumstances.
[0058] The governor of Figure 3 may also be used as a very sensitive pressure reducing valve
as described in connection with the governor of Figure 1, the impulse pipes 49 and
51 both being connected to the same region of the main or pipe, the restriction imposed
by needle valve 52 producing a differential pressure when pressure in the said region
of the main or pipe changes. The characteristic of fluid flow from which the . differential
pressure is derived is thus the rate of change of pressure at the said region of the
main or pipe.
1. Fluid flow control apparatus, for controlling the flow of fluid through a pipe
(26), comprising a fluid flow governor (1); in the pipe (26), a fluid flow control
valve (29) controlled by the governor and producing, in operation, a control pressure
at a predetermined location in the pipe downstream of the valve; and means for producing,
in operation, a differential pressure derived from a characteristic of fluid flow
in the pipe, characterised in that the fluid flow governor comprises a first pressure-responsive
element (5) to which the differential pressure is applied, spring means (7) acting
on the first pressure-responsive element (5) in opposition to the differential pressure,
a second pressure-responsive element (6) to which the control pressure is applied,
means (8) for loading the second pressure-responsive element in opposition to the
control pressure and means for combining displacements of the two pressure-responsive
elements (5, 6) to control the setting of the fluid flow control valve.
2. Fluid flow control apparatus according to claim 1 wherein the characteristic of
fluid flow is the rate of fluid flow through the pipe and the means for producing
the differential pressure comprises a device (37) producing (in operation) a pressure
which is lower than a pressure upstream of the device (37) (the higher pressure),
the higher pressure and the lower pressure being applied to opposed areas of the first
pressure-responsive element (5), the resultant fluid pressure acting on the first
pressure-responsive element being the differential pressure.
3. Fluid flow control apparatus according to claim 1 wherein the characteristic of
fluid flow is the rate of change of fluid pressure at a specified region in the pipe
and the means for producing the differential pressure comprises two impulse connections
(17, 20 or 49, 51), one to each of opposed areas of the first pressure-responsive
element, from the specified region of the pipe, one of the impulse connections including
restricting means (18; 52) for producing at the first pressure-responsive element
on change of pressure at the region, in operation, a pressure which is lower than
the pressure (the higher pressure) in the other impulse connection, the difference
between the higher pressure and the lower pressure being the differential pressure.
4. Fluid flow control apparatus according to any preceding claim which further comprises
an impulse connection (17 or 51) including a throttling device (18 or 52) through
which the fluid pressure is applied to the first pressure-responsive element (5).
5. A fluid flow governor for use in fluid flow control apparatus for controlling the
flow of fluid through a pipe which includes a fluid flow control valve which the governor
is adapted to control and means in the pipe for producing, in operation, a differential
pressure derived from a characteristic of fluid flow in the pipe, the governor being
characterised in that it comprises a first pressure-responsive element (5), spring
means (7) for biassing the first pressure-responsive element, a second pressure-responsive
element (6), means (8) for loading the second pressure-responsive element, means (17,
20 or 49, 51) for enabling the differential pressure to be applied to the first pressure-responsive
element (5) in opposition to the spring means (7), means (17 or 47) for enabling a
control pressure to be applied to the second pressure-responsive element (6) in opposition
to the loading thereon and means for combining displacements of the two pressure-responsive
elements and adapted to control the setting of the fluid flow control valve.
6. Fluid flow control apparatus or governor according to any preceding claim wherein
the displacement of the two pressure-responsive elements are combined at actuating
means (11) coupled to the fluid flow control valve (29) or to servo means (14, 35,
36) for actuating the fluid flow control valve (29).
7. Fluid flow control apparatus or governor according to claim 6 wherein the first
pressure-responsive element (5) is operatively coupled to the actuating means (11)
and the second pressure-responsive element (6) is operatively coupled to the first
pressure-responsive element (5) through the spring means (7), the first (5) and second
(6) pressure-responsive elements being open to a first chamber (16) in the sense that
in operation forces on the pressure-responsive elements due to pressure in the first
chamber oppose the spring means (7), the first pressure-responsive element (5) being
open to a second chamber (19) in the sense that, in operation, the first pressure-responsive
element (5) is subjected to the differential pressure resulting from the difference
in pressures in the first (16) and second (19) chambers, and the second pressure-responsive
element (6) being loaded (8) in the sense to oppose, in operation, pressure applied
to the second pressure-responsive element (6) in the first chamber (16).
8. Fluid flow control apparatus or governor according to any one of preceding claims
1 to 5 wherein the displacements of the two pressure-responsive elements (5, 6) are
combined at fluid flow valve means (14) having first and second relatively movable
elements which co-operate to define a closed or neutral position, the first pressure-responsive
element (5) being operatively connected to the first relatively movable element and
the second pressure-responsive element (6) being operatively connected to the second
relatively movable element.
9. Fluid flow control apparatus or governor according to claim 14 wherein the relatively
movable e..ements are a valve body (22) and a valve member (13) movable therein.
10. Fluid flow control apparatus or governor according to any preceding claim wherein
the pressure-responsive elements (5, 6) are of equal effective area.
11. Fluid flow control apparatus or governor according to any preceding claim wherein
the spring means (7) is a coil spring normally loaded in tension but capable of transmitting
a compressive load, in the manner of a strut.
12. Fluid flow control apparatus or governol according to any preceding claim wherein the second pressure-responsive element (6)
is loaded by a compression spring (8) of which the stiffness is within the range of
two to eight times the stiffness of the spring means
(7).